As the saving of energy became increasingly important, many different kinds of rotary regenerative exchangers were developed in the air conditioning industry for reducing the waste of energy when heating or cooling fresh air introduced in the conditioned space. The purpose of these exchange wheels is to transfer sensible and latent heat from the evacuated air to the fresh air by rotating an exchange wheel through which is flowing the exhaust air, in one half thereof, and the fresh air, in the other half thereof. The exchange wheels, currently found on the market, are made with a plurality of layers of a porous material through which air can flow and sensible and latent heat can be accumulated.
The exchange wheels are generally suitable for all seasons. During cool periods, the evacuated air transfers some of its sensible and latent heat to portions of the wheel through which the exhaust air flows. Since the wheel is rotating, these portions will eventually be in the flow of fresh air and will then transfer the accumulated sensible and latent heat to the fresh air, thereby reducing the heating and humidifying loads for conditioning the conditioned space.
During warm periods, the fresh air transfers some of its sensible and latent heat to portions of the wheel through which the exhaust air flows. As aforesaid, the wheel is rotating and these portions will eventually be in the flow of the exhaust air and will then transfer the accumulated sensible and latent heat to the exhaust air. The fresh air introduced in the conditioned space is then cooler and dryer, thus reducing the cooling load for conditioning the conditioned space.
Examples of rotary exchange wheels are found in U.S. Pat. Nos. 3,945,430, 4,473,108, 4,924,934 and 4,960,166.
The main drawback of existing rotary regenerative exchangers is that they are generally independent devices requiring additional air ducts for connection with the usual conditioning systems as the ones found in buildings. When installed on a rooftop, they require an additional hole with a supporting structure for reinforcing the surrounding of the hole in compensation of the additional weight. This is particularly costly and complicated if a rotary regenerative exchanger has to be installed on an existing air conditioning system because modifications of the ductwork and the roof structures are costly and not always easy to do.